The prominent Conservative MP Jacob Rees-Mogg has become embroiled in a race row after he spoke at a dinner organised by an extreme right-wing group which backs the repatriation of ethnic minority Britons.

Mr Rees-Mogg spoke of his shock of learning about the views of the Traditional Britain Group which this week called for Doreen Lawrence, mother of the murdered black teenager Stephen Lawrence, to leave the country.

However, it has emerged that the MP had been warned about the group by Searchlight, the anti-fascist organisation, the day before his speech and still decided to deliver it. The organisation describes itself as a “home to the disillusioned patriot”.

In a recent online post, it fiercely condemned the peerage awarded last week to Mrs Lawrence. It said: “It is a monstrous disgrace that this Lawrence woman, who is no friend of Great Britain, and who is totally without merit, should be recognised like this or in any other way. In fact she, along with millions of others, should be requested to return to their natural homelands.”

The post referred to a Tory backbencher, Nadhim Zahawi, as “a foreign Conservative Party MP”, and to the shadow Business Secretary, Chuka Umunna, who was born and raised in south London, as a Nigerian. The group’s posts have also quoted Marine Le Pen, the leader of France’s far-right National Front, and denounced adoption by gay partners as “completely obscene”.

Mr Rees-Mogg, the MP for North East Somerset, has distanced himself from the group, although he confirmed he had been warned about their views ahead of his appearance at a London club in May. He said: “I made, in the limited time available, some investigation into these and put them to the organiser of the dinner.” He denied that the Traditional Britain Group held such views and told me that it was a smear.

“My assistant also contacted [Conservative] Central Office who had no knowledge of the group which they could give me,” he added. Mr Rees-Mogg said he was shocked by the group’s comments on repatriation and pointed out they had been after his speech.

He said: “I am shocked by the comments which I note from the Liberal Conspiracy website seem to have been made after I had addressed the dinner. I can entirely dissociate myself from the Traditional Britain Group as I have never been a member or supporter.”

Labour MP Sheila Gilmore said: “It’s shocking that a Conservative MP would associate himself with a group which has such extreme and unpleasant views, despite reportedly being warned by Searchlight. Jacob Rees-Mogg has made a serious error of judgement and must explain why he appears to have ignored Searchlight’s warning.”

She added: “Condoning views like these is not harmless fun or mild eccentricity – it is deeply offensive and shows a lack of respect and common sense. It’s yet another example of a Tory who is completely out of touch with modern Britain.”

In a statement on its website, the group said it believed “exiting the EU and halting immigration are crucial to the survival of the British nation”. Adding: “One appreciates this upsets the liberal-left but we should be permitted to entertain our own opinions, just as they are, without being smeared as ‘far-right’.

“It is clear that people across the political spectrums [sic] among the man-in-the-street are concerned about immigration.”

The statement said Mr Rees-Mogg had made an “excellent speech on a range of issues”. It added: “Only one person present asked about immigration levels etc and Mr Rees-Mogg gave an assimilationist response.”